[PATCH v2 11/11] x86/hyperv: Mark hv_ghcb_terminate() as noreturn

From: Josh Poimboeuf
Date: Wed Apr 12 2023 - 19:50:31 EST


From: "Guilherme G. Piccoli" <gpiccoli@xxxxxxxxxx>

Annotate the function prototype and definition as noreturn to prevent
objtool warnings like:

vmlinux.o: warning: objtool: hyperv_init+0x55c: unreachable instruction

Also, as per Josh's suggestion, add it to the global_noreturns list.
As a comparison, an objdump output without the annotation:

[...]
1b63: mov $0x1,%esi
1b68: xor %edi,%edi
1b6a: callq ffffffff8102f680 <hv_ghcb_terminate>
1b6f: jmpq ffffffff82f217ec <hyperv_init+0x9c> # unreachable
1b74: cmpq $0xffffffffffffffff,-0x702a24(%rip)
[...]

Now, after adding the __noreturn to the function prototype:

[...]
17df: callq ffffffff8102f6d0 <hv_ghcb_negotiate_protocol>
17e4: test %al,%al
17e6: je ffffffff82f21bb9 <hyperv_init+0x469>
[...] <many insns>
1bb9: mov $0x1,%esi
1bbe: xor %edi,%edi
1bc0: callq ffffffff8102f680 <hv_ghcb_terminate>
1bc5: nopw %cs:0x0(%rax,%rax,1) # end of function

Reported-by: Arnd Bergmann <arnd@xxxxxxxx>
Link: https://lore.kernel.org/r/9698eff1-9680-4f0a-94de-590eaa923e94@xxxxxxxxxxxxxxxx/
Signed-off-by: Guilherme G. Piccoli <gpiccoli@xxxxxxxxxx>
Reviewed-by: Michael Kelley <mikelley@xxxxxxxxxxxxx>
Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
---
arch/x86/hyperv/ivm.c | 2 +-
arch/x86/include/asm/mshyperv.h | 2 +-
tools/objtool/check.c | 1 +
3 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/hyperv/ivm.c b/arch/x86/hyperv/ivm.c
index 1dbcbd9da74d..4f79dc76042d 100644
--- a/arch/x86/hyperv/ivm.c
+++ b/arch/x86/hyperv/ivm.c
@@ -127,7 +127,7 @@ static enum es_result hv_ghcb_hv_call(struct ghcb *ghcb, u64 exit_code,
return ES_OK;
}

-void hv_ghcb_terminate(unsigned int set, unsigned int reason)
+void __noreturn hv_ghcb_terminate(unsigned int set, unsigned int reason)
{
u64 val = GHCB_MSR_TERM_REQ;

diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
index 4c4c0ec3b62e..09c26e658bcc 100644
--- a/arch/x86/include/asm/mshyperv.h
+++ b/arch/x86/include/asm/mshyperv.h
@@ -212,7 +212,7 @@ int hv_set_mem_host_visibility(unsigned long addr, int numpages, bool visible);
void hv_ghcb_msr_write(u64 msr, u64 value);
void hv_ghcb_msr_read(u64 msr, u64 *value);
bool hv_ghcb_negotiate_protocol(void);
-void hv_ghcb_terminate(unsigned int set, unsigned int reason);
+void __noreturn hv_ghcb_terminate(unsigned int set, unsigned int reason);
#else
static inline void hv_ghcb_msr_write(u64 msr, u64 value) {}
static inline void hv_ghcb_msr_read(u64 msr, u64 *value) {}
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 8586d4c36600..e23d12041be0 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -213,6 +213,7 @@ static bool __dead_end_function(struct objtool_file *file, struct symbol *func,
"ex_handler_msr_mce",
"fortify_panic",
"hlt_play_dead",
+ "hv_ghcb_terminate",
"kthread_complete_and_exit",
"kthread_exit",
"kunit_try_catch_throw",
--
2.39.2